In a thermal power plant or a chemical plant, many pipes are routed and arranged, and many tanks are installed. In this case, one of the pipes and another of the pipes may be connected by flanges for convenience in connecting the pipes. Also, a manhole of a tank and a cover for closing the manhole may be connected by flanges.
FIG. 9 shows a conventional flange connection structure to be applied to piping or a pipe. As shown in the drawing, a flange 2 is formed on one pipe 1, and a flange 4 is formed on another pipe 3. A gasket is interposed between a flange surface of the flange 2 and a flange surface of the flange 4, and the flanges 2 and 4 are fastened by bolts (not shown), whereby the flange surface of the flange 2 and the flange surface of the flange 4 are joined together. By so doing, the pipe 1 and the pipe 4 are coupled together.
If the pipes 1 and 3 are coupled by such a flange connection structure, it suffices to loosen and detach the bolts fastening the flanges 2 and 4, when releasing the pipes 1 and 3 for maintenance, inspection or cleaning. By this measure, the pipes 1 and 3 can be released.
In restoring the pipes 1, 3 to the original state, it is enough to perform the simple work of fastening the flanges 2 and 4 by bolts.
FIG. 10 shows a conventional flange connection structure to be applied to a tank. As shown in the drawing, a flange 12 is formed on a manhole 11 of a tank 10, and a flange 14 is formed on a cover 13. A gasket is interposed between a flange surface of the flange 12 and a flange surface of the flange 14, and the flanges 12 and 14 are fastened by bolts (not shown), whereby the flange surface of the flange 12 and the flange surface of the flange 14 are joined together. By so doing, the manhole 11 is closed by the cover 13.
If the manhole 11 is closed with the cover 13 according to such a flange connection structure, it suffices to loosen and detach the bolts fastening the flanges 12 and 14, when allowing access to the interior of the tank 10 for maintenance, inspection or cleaning. By this measure, the tank 10 can be opened.
In restoring the tank to the original state, it is enough to perform the simple work of fastening the flanges 12 and 14 by the bolts.    Patent Document 1: JP-A-2001-289331